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fine oxide about 0*2 gram of powdered substance (acctanilide
may be conveniently used, see Prep. 54,  p.   151)   is weighed
out by difference from a sample tube, which should contain the
approximate quantity.    The substance is then well mixed with
the oxide by shaking the flask.     The contents of the flask are
carefully poured into the tube above the  coarse oxide  in  the
manner described and the flask is rinsed out with coarse oxide,
which is likewise poured into the tube until it is filled to the
full length of the furnace.     A loose plug of asbestos is pushed
in to keep the materials in position and the tube is   tapped
horizontally on the bench in order to form a channel above the
layer of fine copper oxide.    The tube is now laid in the furnace,
which is tilted a little forwards in order to collect the moisture
at  the front end   of the   tube.     The   short   closed   tube  is
well packed with powdered  sodium   bicarbonate  and   tapped
horizontally so as to form a good  channel   above  the   whole
length of the substance.    It is laid in the small furnace, which
is also tilted forwards to drain off the water which is formed.
The bicarbonate and the combustion tubes are connected by the
bulb tube already described.    The copper spiral is now reduced
and pushed into the front of the tube up to the plug and finally
the azotometer is attached by its bent tube.    The arrange men t
of the tubes and their contents are shown in Figs. 13 and 15.

The Combustion.—The tap of the azotometer is opem-cl
and the reservoir lowered so as to empty as far as possible the

COARSE   —   CuO




JIG. 15.


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